I put TKD volume pot and AudioNote Copper caps in an older Cary Audio SLP94 preamp and it was a nice upgrade over stock.
I think as others have said it really depends on what your looking for but yes changing a few key components can change the sound if its an improvement or not is up to your ears and what yo like. it could be a fun experiment if your handy with a soldering iron to change out key components with others. I've always wanted to try a bunch of different caps etc.